Helicopters usually include a load attachment coupling in substantial alignment with the axis of rotation of the main lifting rotor. Such a system, referred to for convenience as a lifting hook or lifting point, and referred to herein as a standard lifting hook attachment, is satisfactory for most applications where a vertical lift is required. Vertical loads are sometimes lifted directly abeam the main rotor to provide for loading and unloading of the helicopter whilst in flight. Helicopters have also been used for hauling non-vertical loads, such as hauling cable. For example, in the construction and maintenance of power transmission cables, helicopters have on been used, particularly over precipitous or difficult terrain. However, the load that can be hauled by helicopter has been limited, and has been found to be considerably less than the vertical lifting capacity of the helicopter. Additionally, controlling the helicopter whilst hauling a non-vertical load has been found to be difficult.
A system using a mounting coupling mounted to the lifting hook (or the mounting for the lifting hook) has been used as described in Australian Patent Application No. 2006203572. However, such an arrangement fails to recognize or understand the effect of applying loads with non vertical components to an aircraft operating in a complex three dimensional equilibrium condition. As a result, operation of the aircraft using this arrangement causes significant and undesirable rolling under application of external hauling loads. The chosen attachment position also generates a requirement to provide more power to the tail rotor to maintain stability of the helicopter under normal operating conditions, further limiting hauling capacity and range of hauling angles available. Pilot visibility of the load being hauled and pilot comfort are also impaired in this arrangement. If a pilot attempts to direct the load forward, then more control input is required with a consequential loss of available power for hauling. If a pilot attempt to direct the load aft, there is a risk that the cable could contact the tail rotor and cause the aircraft to crash.
The present invention aims to provide a load attachment system for helicopters which alleviates one or more of the problems of the prior art. Other aims and advantages of the invention may become apparent from the following description.